Coccidiosis is a widespread disease of acute economic concern to the poultry industry. The invasive intestinal infection is caused by one or more of several species of Eimeria that invade the digestive tract of birds, causing depressed weight gain, intestinal and cecal lesions, depigmentation and poor feed conversion. Economic losses to the poultry industry from this disease have been estimated to be as high as $300 million annually (Danforth, H. D., and P. C. Augustine, 1985, "Use of hybridoma antibodies and recombinant DNA technology in protozoan vaccine development," Avian Diseases, 30:37-42). Current coccidiostatic and coccidiocidal medications to combat this disease add another $100 million in annual production costs to the poultry industry. Due to evidence of increasing resistance to currently marketed anticoccidial-drugs, immunological techniques to create a vaccine against the parasites are being investigated by various groups.
Certain regions on the cell surface of the coccidial parasite have been shown to possess discrete immunogenic properties (Danforth, et al., 1985). Because subunit techniques have proved to be a successful method of inducing partial or complete immunity against a variety of antigens, the molecular manipulation of Eimeria immunogenic regions to induce an immune response in the host has been tested as an anti-coccidial approach.
Due to the logistical difficulties inherent in the isolation of native Eimeria cell surface proteins in sufficient quantities to permit characterization and testing for vaccine efficacy, workers have utilized the biotechnological isolation of the gene(s) coding for these antigenic proteins to produce mass quantities of recombinant antigenic protein in host bacterial or yeast cells. Recombinant anticoccidial vaccines are currently under study by numerous groups. Most of these vaccines have demonstrated the ability to reduce intestinal lesions or oocyst excretion in challenge studies. While similar recombinant techniques and procedures were employed by these workers to synthesize each of the proteins, each vaccine may be differentiated with statistical certainty based on the amino acid sequences of the different recombinant immunogens.
Danforth, et al., (1985) discloses a recombinant coccidial protein which provides partial protection against coccidial infection by a particular Eimeria species. The article does not teach that the protein provides cross-protection against other coccidial species.
Kim et al., 1989, Infection and Immunity, vol. 57, pp. 2434-40, teaches cloned p250 surface antigen of Eimeria acervulina merozoites. Upon inoculation with transformed E. coli carrying the cloned antigen, partial protection was achieved. The plasmid carrying the cloned antigen gene survived in the intestinal flora, even after the E. coli which initially harbored the plasmid were no longer present.
Miller, 1989 Infection and Immunity, vol. 57, pp. 2014-20, discloses a cloned protein from Eimeria tenella which was identified using an antibody raised against E. acervulina sporozoites. Live recombinant E. coli harboring the gene for the cloned protein provided a degree of partial protection.
Clarke, et al., 1989, Molecular and Biochemical Parasitology, vol. 22, pp. 79-87, reports the identification of a substantial number of DNA sequences (24), ceding for antigens of E. tenella, by direct screening of genomic libraries with immune serum. No protective effects were reported for any of these antigens.
Australian Patent Application of Merck & Co., AU-A28542/89 discloses E. tenella recombinant protein immunogens. The sequence of at least one such immunogen is disclosed.
Australian Patent Application AU-A-65869/86 of Solvay and Cie, discloses a cloned antigen which confers immunity against Elmeria tenella, Elmeria necatrix and Eimeria maxima. The antigen comprises two polypeptides joined by a disulfide bond and having molecular weights of about 17,000 and 8,000, respectively.
International Patent Application No. WO 90/00403 of Genex Corporation discloses a cloned gene encoding an antigenic protein found in avian coccidial. Seven different sequences are disclosed which are immunoreactive with antibodies against coccidia.
European Publication No. 0 349 071 of Akzo N.V. discloses a polypeptide of Eimeria which can be used to immunize poultry. Molecular clones were isolated from both E. acervulina and E. tenella.
European Publication No. 0 344 808 of F. Hoffman-la Roche AG discloses cloned antigens for protection against coccidiosis. Sequences of the antigens are disclosed.
European Publication No. 0 324 648 of Merck & Co. discloses cloned genes coding for Group A, C, F, and H Eimeria tenella immunogens.